ASoC: arizona: Fix gain settings of FLL in free-run mode

The wrong register was used to set the gain of ref loop, when changing
the FLL output on an active FLL. This patch corrects the offset of the
gain register.

Signed-off-by: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org